/*
 * Copyright (C) 2008 The Guava Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.google.common.testing;

import com.google.common.annotations.Beta;
import com.google.common.annotations.GwtCompatible;

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.logging.Handler;
import java.util.logging.LogRecord;
import javax.annotation.CheckForNull;

/**
 * Tests may use this to intercept messages that are logged by the code under test. Example:
 *
 * <pre>
 *   TestLogHandler handler;
 *
 *   protected void setUp() throws Exception {
 *     super.setUp();
 *     handler = new TestLogHandler();
 *     SomeClass.logger.addHandler(handler);
 *     addTearDown(new TearDown() {
 *       public void tearDown() throws Exception {
 *         SomeClass.logger.removeHandler(handler);
 *       }
 *     });
 *   }
 *
 *   public void test() {
 *     SomeClass.foo();
 *     LogRecord firstRecord = handler.getStoredLogRecords().get(0);
 *     assertEquals("some message", firstRecord.getMessage());
 *   }
 * </pre>
 *
 * @author Kevin Bourrillion
 * @since 10.0
 */
@Beta
@GwtCompatible
public class TestLogHandler extends Handler
{
    /**
     * We will keep a private list of all logged records
     */
    private final List<LogRecord> list = new ArrayList<>();

    /**
     * Adds the most recently logged record to our list.
     */
    @Override
    public synchronized void publish(@CheckForNull LogRecord record)
    {
        list.add(record);
    }

    @Override
    public void flush()
    {
    }

    @Override
    public void close()
    {
    }

    public synchronized void clear()
    {
        list.clear();
    }

    /**
     * Returns a snapshot of the logged records.
     */
    /*
     * TODO(cpovirk): consider higher-level APIs here (say, assertNoRecordsLogged(),
     * getOnlyRecordLogged(), getAndClearLogRecords()...)
     *
     * TODO(cpovirk): consider renaming this method to reflect that it takes a snapshot (and/or return
     * an ImmutableList)
     */
    public synchronized List<LogRecord> getStoredLogRecords()
    {
        List<LogRecord> result = new ArrayList<>(list);
        return Collections.unmodifiableList(result);
    }
}
